1. Field of the Invention
This invention relates the level sensor, and more particularly to a level sensor for detecting of a level of a liquid or powdered material.
2. Description of the Prior Art
A conventional level sensor comprises level detection resistors, a temperature compensation resistor having the same temperature characteristic as those of the level detection resistors, and two resistance measurement circuits for measuring resistance values of the level detection resistors and the temperature compensation resistor, respectively. In this instance, the temperature compensation resistor is coated with an insulating material in order to allow it to be electrically isolated from the level detection resistors.
In a sensor where the level detection resistors are short-circuited, e.g., by an electrolyte contained in a vessel, when the liquid level changes in a range from the lower end portion of the level detection resistor to the upper end portion thereof, the resistance value outputted from the resistance measurement circuit connected to the level detection resistors changes linearly.
Thus, the liquid level is detected by the resistance value mentioned above.
The slope of the straight line indicating the relation between the resistance value and the liquid level depends on temperature because of the temperature characteristic of the level detection resistor. Namely, the resistance value is changed not only by the liquid level but also by temperature.
In view of this, the conventional level sensor further comprises a computation circuit (or a processor) for reading thereinto a resistance value outputted from the resistance measurement circuit connected to the temperature compensation resistor to perform a temperature compensating operation on the basis of the resistance value thus read thereinto.
However, since the above-mentioned conventional level sensor requires two resistance measurement circuits and a computation circuit (or processor), there was the problem that its construction is complicated, and the cost is increased.